Light emitting device and manufacturing method thereof

ABSTRACT

An element structure is provided in which film formation irregularities and deterioration of an organic compound layer formed on an electrode are prevented in an active matrix light emitting device. After forming an insulating film so as to cover edge portions of a conductor which becomes a light emitting element electrode, polishing is performed using a CMP (chemical mechanical polishing) method in the present invention, thus forming a structure in which surfaces of a first electrode and a leveled insulating layer are coplanar. The film formation irregularities in the organic compound layer formed on the electrode can thus be prevented, and electric field concentration from the edge portions of the electrode can be prevented.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a light emitting device with alight emitting element that emits fluorescent light or phosphorescentlight upon application of electric field to a pair of electrodes of theelement which sandwich a film containing an organic compound (the filmis hereinafter referred to as organic compound layer), and to a methodof manufacturing the light emitting device. Incidentally, in the presentspecification, the light emitting device indicates an image displaydevice or a plane emission device using a light emitting element as alight emitting element. Besides, the light emitting device includes amodule in which a FPC (Flexible Printed Circuit), a TAB (Tape AutomatedBonding) tape, or a TCP (Tape Carrier Package) is attached to asubstrate over which a light emitting element is formed, a module inwhich a printed wiring board is provided at an end of a TAB tape or aTCP, and a module in which an IC (Integrated Circuit) is directlymounted on a substrate over which a light emitting element is formed bya COG (Chip On Glass) system.

[0003] 2. Description of the Related Art

[0004] Light emitting elements, which employ organic compounds as lightemitting member and are characterized by their thinness and lightweight, fast response, and direct current low voltage driving, areexpected to develop into next-generation flat panel displays. Amongdisplay devices, ones having light emitting elements arranged to form amatrix shape are considered to be particularly superior to theconventional liquid crystal display devices for their wide viewing angleand excellent visibility.

[0005] It is said that light emitting elements emit light through thefollowing mechanism: a voltage is applied between a pair of electrodesthat sandwich an organic compound layer, electrons injected from thecathode and holes injected from the anode are re-combined at theluminescent center of the organic compound layer to form molecularexcitons, and the molecular excitons return to the base state whilereleasing energy to cause the light emitting element to emit light.Known as excitation states are singlet excitation and tripletexcitation, and it is considered that luminescence can be conductedthrough either one of those excitation states.

[0006] Such light emitting devices having light emitting elementsarranged to form a matrix can employ passive matrix driving (simplematrix light emitting devices), active matrix driving (active matrixlight emitting devices), or other driving methods. However, if the pixeldensity is large, active matrix light emitting devices in which eachpixel (or each dot) has a switch are considered as advantageous becausethey can be driven with low voltage.

[0007] An active matrix type light emitting device structured by that athin film transistor (hereinafter, referred to as TFT) is formed on theinsulating surface, an interlayer insulating film is formed thereon, andthat the first electrode of a light emitting element connectedelectrically to the TFT through the interlayer insulating film.

[0008] In addition, an organic compound layer is formed on the firstelectrode. The organic compound layer includes a hole injection layer, ahole transporting layer, a light emitting layer, a blocking layer, anelectronic transporting layer, and an electronic injection layer. Theorganic compound layer can be formed by a single layer, however, it canalso be formed by combining above-mentioned plural layers. A lightemitting element is formed by that the second electrode is formed afterthat the organic compound layer is formed.

[0009] When these electrodes are anodes, metals having a large workfunction are used as an electrode material for an improvement of holeinjection from an anode to an organic compound layer. It is noted that awork function of ITO is 4.8 eV, that is made frequently use as an anodematerial. On the other hand, in the case that these electrodes are acathode, small work function metals or alloy containing said metals arerespectively used for an improvement of electron injection from acathode to an organic compound layer, because a great deal of organiccompound has a small electron affinity in comparison with metals orinorganic semiconductors. Typically, as metals having small workfunction, one is belonging Group 1 or Group 2 in periodic table of theelement is preferable to be used.

[0010] In an active matrix type light emitting device, in the case thata luminescence is extracted from a light emitting element connectedelectrically to TFT on the substrate across the substrate, (for example,unexamined patent publication Nos. 6-325869, 7-153576, and 8-241047), itis limited to the region where the light emitting region is formed ineach pixel of TFT, wiring and the like. Therefore, it produces a problemthat a rate of light emitting region (an aperture ratio) having a placein the pixel region become small.

[0011] In order to solve the problem, in the case that light generatedfrom a light emitting element is emitted from a face opposed to thesubstrate where the light emitting element is formed thereon(hereinafter, referred to as an upward emission), for example, it isdisclosed in unexamined patent publication Nos. 7-111341, 8-54836, and10-189252, problems due to an aperture ratio can be prevented.

[0012] However, in any case of above-mentioned structures, the firstelectrode electrically connected to a TFT is formed on the interlayerinsulating film covering TFT, so that the face has irregularities. Atthis time, an organic compound layer of a light emitting element with athickness of 20 to 200 nm formed on an electrode is so thin that make adifference in level when an electrode is formed, and that result toproduce a defective deposition in the organic compound layer formed onthe difference level. The portion of a defective deposition is cause toshort-circuit between the first electrode forming a light emittingelement and the second electrode formed on the organic compound layer.Therefore, there are some cases that the method structured by that theedge portion of the first electrode is covered by an insulating film isadopted.

[0013] In addition, in the forming step of the second electrode, in theparticular case that the light is emitted from the second electrodeside, the thickness should be thin not to deteriorate the transmittance.Similarly, a level difference due to the first electrode may be a causeof deposition deterioration in forming of the second electrode.

[0014] A transparent conductive film needs to be formed above theorganic compound layer in order to emit light from opposite face to thesubstrate. However, a problem is occurred that necessity of high energyto form the film is severely damage the organic compound layer.

SUMMARY OF THE INVENTION

[0015] The object of the present invention is to prevent a deteriorationof a film deposition of an organic compound layer formed on an electrodeby forming the structure that seldom has a difference of level betweenan electrode formed face and an electrode when an electrode is formed inmanufacturing step of a light emitting device. Further, a structure inwhich concentration of electrical field is never occurred ismanufactured thereby enabling to provide a long-living light emittingdevice in which the light emitting element is hardly deteriorated.

[0016] There is a danger that an electric field concentration may occurfrom an edge portion of a first electrode, and an organic compound layerformed on the first electrode may deteriorate, and there is a dangerthat film formation irregularities may develop when forming the organiccompound layer due to roughness formed when there is a step in the edgeportion of the first electrode, and when the edge portion of the firstelectrode is covered by an insulating film. The applicant of the presentinvention therefore considers forming an insulating layer that contactsthe edge portion of the first electrode and is coplanar with a surfaceof the first electrode.

[0017] The applicant of the present invention also considers polishingby using CMP (chemical mechanical polishing) after forming theinsulating film so as to cover the edge portion of a conductor thatbecomes the first electrode, and forming the first electrode and aleveled insulating layer on the same plane.

[0018] CMP is a method in which a surface of a workpiece to be polishedis taken as a standard, and leveling is performed chemically ormechanically on the surface by following the standard. Generally, apolishing cloth or a polishing pad (hereinafter referred to genericallyas “pad” in this specification) is attached to a platen or a polishingplate. The platen and the workpiece to be polished are then each rotatedor oscillated, while supplying slurry between the workpiece and the pad.Polishing of the surface is thus performed by a compound chemical andmechanical action.

[0019] The first electrode and the leveled insulating layer can beformed on the same plane, and deterioration and film formingirregularities that follow electric field concentration of the organiccompound layer formed on the first electrode can be prevented, inaccordance with the above structure. Note that a state in which aconductive film that becomes the first electrode has been patterned isreferred to as a conductor within this specification, and that theconductor is referred to as the first electrode after undergoing thepolishing process by the CMP method. In addition, the insulating filmformed so as to cover the conductor is referred to as the leveledinsulating layer after undergoing polishing process by the CMP method.

[0020] Further, in addition to the aforementioned structure, not onlycan an element structure be formed in which light emission developing inthe organic compound layer is emitted toward the substrate from thefirst gate electrode side of the light emitting element, but it alsobecomes possible to form a light emitting element, without taking intoaccount the aperture ratio, by forming an element structure in whichlight is emitted in a direction opposite that of the substrate from asecond electrode side formed on the organic compound layer.

[0021] Additionally, although it is necessary to form the secondelectrode by using a transparent conductive film having lighttransmitting characteristics when forming an upper surface emissionstructure, sputtering damage during film formation of the secondelectrode can be prevented by forming the second electrode usingevaporation and by forming a barrier film in advance.

[0022] Furthermore, with the elements of the present invention, thesecond electrode can be formed without causing film formingirregularities, even if it is necessary to form a thin film due toqualities such as material transmittivity and resistivity when formingthe second electrode in order to give it a flat structure.

[0023] A structure of the present invention disclosed in thisspecification relates to a method of manufacturing a light emittingdevice, characterized by comprising:

[0024] forming a thin film transistor on a substrate;

[0025] forming an insulating layer covering the thin film transistor;

[0026] forming a wiring through the insulating layer;

[0027] forming a conductor, which is electrically connected to the thinfilm transistor by the wiring, on the insulating layer;

[0028] forming an insulating film covering the conductor;

[0029] polishing the conductor and the insulating film by a CMP method,thus forming a first electrode and a leveled insulating layer;

[0030] forming an organic compound layer contacting the first electrode;and

[0031] forming a second electrode contacting the organic compound layer;

[0032] in which the first electrode and the leveled insulating filmformed by the CMP method form the same plane.

[0033] Also, another structure of the present invention disclosed inthis specification relates to a method of manufacturing a light emittingdevice, characterized by comprising:

[0034] forming a thin film transistor on a substrate;

[0035] forming an insulating layer covering the thin film transistor;

[0036] forming a wiring through the insulating layer;

[0037] forming a conductor, which is electrically connected to the thinfilm transistor by the wiring, on the insulating layer;

[0038] forming an insulating film covering the conductor;

[0039] polishing the conductor and the insulating film by a CMP method,thus forming a first electrode and a leveled insulating layer;

[0040] forming an organic compound layer contacting the first electrode;and

[0041] forming a second electrode contacting the organic compound layer;

[0042] in which the organic compound layer is formed so as to completelycover the first electrode.

[0043] Further, another structure of the present invention disclosed inthis specification relates to a method of manufacturing a light emittingdevice, characterized by comprising:

[0044] forming a thin film transistor on a substrate;

[0045] forming an insulating layer covering the thin film transistor;

[0046] forming a wiring through the insulating layer;

[0047] forming a conductor, which is electrically connected to the thinfilm transistor by the wiring, on the insulating layer;

[0048] forming an insulating film covering the conductor;

[0049] polishing the conductor and the insulating film by a CMP method,thus forming a first electrode and a leveled insulating layer;

[0050] forming an organic compound layer contacting the first electrode;and

[0051] forming a second electrode contacting the organic compound layer;

[0052] in which the organic compound layer is formed contacting thefirst electrode and the leveled insulating layer.

[0053] In each of the above structures, the method is characterized inthat the first electrode and the leveled insulating film formed bypolishing by a CMP method have a film thickness of from 50 to 500 nm.

[0054] Further, a structure of the present invention disclosed in thisspecification relates to a light emitting device including:

[0055] a first electrode having an edge portion;

[0056] a leveled insulating film formed contacting the edge portion ofthe first electrode;

[0057] an organic compound layer; and

[0058] a second electrode;

[0059] characterized in that:

[0060] surfaces of the first electrode and the leveled insulating layerare coplanar;

[0061] the organic compound layer contacts the first electrode; and

[0062] the second electrode contacts the leveled insulating layer andthe organic compound layer.

[0063] Further, another structure of the present invention disclosed inthis specification relates to a light emitting device including:

[0064] a thin film transistor;

[0065] a wiring;

[0066] a first electrode having an edge portion;

[0067] a leveled insulating layer formed contacting the edge portion ofthe first electrode;

[0068] an organic compound layer; and

[0069] a second electrode;

[0070] formed on a substrate;

[0071] characterized in that:

[0072] the first electrode is electrically connected to the thin filmtransistor through the wiring;

[0073] surfaces of the first electrode and the leveled insulating layerare coplanar;

[0074] the organic compound layer contacts the first electrode; and

[0075] the second electrode contacts the leveled insulating layer andthe organic compound layer.

[0076] In each of the above structures, the thin film transistor is ap-channel thin film transistor in the case where the first electrode isan anode. Further, the thin film transistor is an n-channel type thinfilm transistor in the case where the first electrode is a cathode.

[0077] Furthermore, it is preferable that a material having a large workfunction be used as a material for forming the first electrode in thecase where the first electrode is the anode. This is because holes areinjected into the organic compound layer from the anode when a voltageis applied, and therefore it is necessary that the first electrodematerial have an HOMO level which is higher than that of the organiccompound forming the organic compound layer. Note that it is preferablethat the first electrode be formed of a low resistance material, becauseit is formed while being connected to a TFT. Materials such as ITO(indium tin oxide) and IZO (indium zinc oxide), which are transparentconductive films, and platinum (Pt), chrome (Cr), tungsten (W), andnickel (Ni) can be used as the specific anode materials which satisfythese conditions.

[0078] Conversely, it is preferable that a material having a small workfunction be used in cases in which the first electrode is the cathode.This is because an electrode having a small work function is necessaryfor electron injection because the electron affinity of many organicmaterials is small compared to metals and inorganic semiconductors.Further, it is preferable that a low resistance material be used for thefirst electrode, because it is formed while being connected to a TFTformed on a substrate.

[0079] Metallic materials such as aluminum, titanium, and tungsten areapplicable as low resistance materials, and an alloy in which a materialbelonging in Group 1 or Group 2 of the periodic table is laminated withthese low resistance materials may be used because a small work functionis required in order to be used as the cathode material. In addition, itis also possible to use a chemical compound such as a fluoride of amaterial belonging in Group 1 or Group 2 of the periodic table.

[0080] Specifically, there are alloys such as: an alloy in which silveris added to magnesium (Mg:Ag), an alloy in which lithium is added toaluminum (Al:Li), and an alloy containing lithium, calcium, andmagnesium in aluminum. Note that the alloys in which lithium is added toaluminum are known to be capable of making the work function of aluminumsmallest.

[0081] Further, in the present invention, after the first electrode isformed, an insulating film made from an insulating material is formed onthe first electrode so as to completely cover the first electrode. Bythen polishing a part of the formed insulating film and the firstelectrode by the CMP method, a structure is formed such that theinsulating film and the first electrode are formed on the same plane.

[0082] Further, in addition to insulating materials containing siliconsuch as silicon oxide, silicon oxynitride, and silicon nitride, organicresin films such as polyimide, polyamide, acrylic (includingphotosensitive acrylics) and BCB (benzocyclobutene) can also be used asthe insulating material used in the insulating film.

[0083] Steps between the first electrode and the insulating film arethus eliminated, and therefore problems such as film formationirregularities arising upon forming an organic compound layer and asecond electrode later can be resolved.

[0084] In addition, by performing the aforementioned processing usingthe CMP method, the film thickness of the organic compound layer formedon the first electrode can be made uniform because the surface of thefirst electrode is leveled, and an electric field can be added uniformlywith respect to the organic compound layer. Note that electric currentdensity is non-uniform in the organic compound layer in the case wherethe electric field is non-uniform, and not only does the luminance of alight emitting element drop, but in addition, a problem arises in thatthe element lifetime is reduced because the element deterioratesquickly. Processing by the CMP method therefore also has an effect ofincreasing the element characteristics by allowing the addition of auniform electric field with respect to the organic compound layer.

[0085] Furthermore, the organic compound layer formed on the firstelectrode is a place at which carriers injected from the cathode and theanode recombine. There is a case in which the organic compound layer isformed by a single layer comprised of only a light emitting layer, butthe present invention also includes a case in which a plurality oflayers such as a hole injecting layer, a hole transporting layer, alight emitting layer, a blocking layer, an electron transporting layer,and an electron injecting layer are laminated and formed as the organiccompound layer. Note that known materials can be used as the materialsemployed when forming these layers during the formation of the organiccompound layer in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] In the accompanying drawings:

[0087]FIGS. 1A to 1D are diagrams for explaining the structure of thepresent invention;

[0088]FIGS. 2A to 2C are diagrams for explaining an element structure ofa light emitting device of the present invention;

[0089]FIGS. 3A and 3B are diagrams for explaining an element structureof the light emitting device of the present invention;

[0090]FIG. 4 is a diagram for explaining an element structure of thelight emitting device of the present invention;

[0091]FIGS. 5A to 5C are diagrams for explaining a process ofmanufacturing the light emitting device of the present invention;

[0092]FIGS. 6A to 6C are diagrams for explaining the process ofmanufacturing the light emitting device of the present invention;

[0093]FIGS. 7A to 7C are diagrams for explaining the process ofmanufacturing the light emitting device of the present invention;

[0094]FIGS. 8A and 8B are diagrams for explaining the process ofmanufacturing the light emitting device of the present invention;

[0095]FIGS. 9A and 9B are diagrams for explaining an element structureof the light emitting device of the present invention;

[0096]FIGS. 10A and 10B are top views of a pixel portion of the lightemitting device;

[0097]FIGS. 11A and 11B are diagrams for explaining an element structureof the light emitting device of the present invention;

[0098]FIGS. 12A and 12B are diagrams for explaining the structure of areverse stagger TFT;

[0099]FIG. 13 is a diagram showing measurement results relating totransmittivity of a light emitting element; and

[0100]FIGS. 14A to 14H are diagrams showing examples of electronicequipment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0101]FIGS. 1A to 1D and 2A to 2C are used in explaining an embodimentmode of the present invention. A light emitting device of the presentinvention is manufactured by a method of manufacturing containing a CMPprocess, explained by FIGS. 1A to 1C, as a portion. Further, FIGS. 2A to2C show an element structure of the light emitting device manufacturedby the present invention.

[0102] In FIG. 1A, a thin film transistor (TFT) 102 is formed on asubstrate 101, and a conductor 105, which is electrically connected tothe thin film transistor 102 by a wiring 104 formed through aninsulating layer 103, is formed.

[0103] An insulating film 106 made from an insulating material is formednext on the conductor 105 so as to cover the conductor 105 as shown inFIG. 1B. Note that the insulating film 106 formed here is formed so asto be thicker than the film thickness obtained when forming theconductor 105 and the wiring 104. Specifically, the insulating film 106is formed to have a thickness of 0.5 to 5 μm. The conductor 105 and thewiring 104 are thus completely covered by the insulating film 106.

[0104] The insulating film 106 and the conductor 105 are then polishedby the CMP method as shown in FIG. 1C. Note that FIG. 1D shows anapparatus for performing polishing by CMP.

[0105] A polishing cloth (also referred to as a pad) 122 is attached toa circular shape rotational platen 121 having a diameter of 80 cm asshown in FIG. 1D. Urethane foam or the like is employed as the materialused in the polishing cloth 122.

[0106] Slurry 124 is then supplied to the center of the rotationalplaten 122 through a pipe 123, and the slurry 124 spreads out over theentire surface of the polishing cloth 122 on the rotational platen 121by the rotation and oscillation of the rotational platen 121. The slurry124 is a colloid solution in which particles, a liquid, and a chemicalagent are mixed. Silica slurry having a pH of 9 to 11 and made from KOHand the like, alumina (Al₂O₃) slurry having a pH of 3 to 4, andmagnesium oxide (MnO₂, Mn₂O₃) slurry can be used for the slurry 124. Thealumina slurry can be used by combining with an agent having oxidizingpower. In addition, it is also possible to use neutral slurry and thelike. Note that the term neutral slurry used here includes slurry formedby silica and water.

[0107] Note that the slurry shown here are only preferable examples, andother known slurry can also be used. Further, the rotational platen 121rotates with its center as a rotational axis 125. Note that therotational speed of the rotational platen 121 is set to be 3 to 10 rpm.

[0108] On the other hand, a glass substrate 127 adheres to a circularshape metallic polishing head 126 having a diameter of 30 cm by vacuumsuction. A wafer suction pad 128 is formed between the glass substrate127 and the polishing head 126. There are holes between the wafersuction pad 128 and the polishing head 126, and the glass substrate 127adheres to the polishing head 126 through the holes. The center of thepolishing head 126 is positioned between the center of the rotationalplaten 121 and the circumference of the rotational platen 121. Thepolishing head 126 is rotated at 10 to 50 rpm with the center of thepolishing head 126 as a rotational axis.

[0109] Note that a pressure of 200 to 400 gf/cm² is applied to the glasssubstrate 127, pushing the glass substrate 127 onto the polishing cloth122 on the rotational platen 121. The polishing rate of the film to bepolished can be regulated by changing the pressure of the polishing head126.

[0110] The polishing time is set to be 1 to 2 minutes. By polishing boththe insulating film 106 and the conductor 105, a first electrode 107 anda leveled insulating film 108 can be formed having an equal filmthickness, as measured from the surface of the insulating film 103, andcan be formed on the same plane.

[0111] Note that known materials can be used for the slurry, the pad,and the like employed in the CMP method explained here. Further, knownmethods can be used for processing conditions and the like.

[0112] Note that the conductor 105 polished by CMP here is referred toas the first electrode 107, and the insulating film 106 polished by CMPhere is referred to as the leveled insulating layer 108. The firstelectrode 107 and the leveled insulating layer 108 formed here have athickness of 50 to 500 nm.

[0113] An organic compound layer (not shown) is then formed on the firstelectrode 107. Note that the organic compound layer is formed so as tocompletely cover the first electrode. In addition, a second cathode (notshown) is formed on the organic compound layer, thereby completing alight emitting element.

[0114] An active matrix light emitting device manufactured by formingthe organic compound layer and the second electrode on the firstelectrode as discussed above is explained in detail in Embodiment Modes1 to 3 below.

[0115] [Embodiment Mode 1]

[0116] A cross sectional structure of a pixel portion of a lightemitting device formed as Embodiment Mode 1 of the present invention isshown in FIG. 2A.

[0117] Thin film transistors (TFTs) are formed on a substrate 201 inFIG. 2A. Note that there are shown here, an electric current control TFT222 which is electrically connected to a first electrode 210 of a lightemitting element 216, and which has a function for controlling electriccurrent supplied to the light emitting element 216, and a switching TFT221 for controlling a video signal applied to a gate electrode of theelectric current control TFT 222.

[0118] A glass substrate is used for the substrate 201 as a substratehaving light transmittance here, and a quartz substrate may also beused. Further, active layer of each TFT is provided with at least achannel forming region 202, a source region 203, and a drain region 204.

[0119] Further, a gate electrode 206 is formed covering a gateinsulating film 205, and overlapping with the channel forming region 202through the gate insulating film 205, in the active layer of each TFT.Furthermore, a first insulating layer 208 is formed covering the gateelectrode 206, and an electrode which is electrically connected to thesource region or the drain region of each TFT is formed on the firstinsulating layer 208.

[0120] Note that the electric current control TFT 222 is formed by ap-channel TFT in Embodiment Mode 1, and the drain region 204 of theelectric current control TFT 222 is connected to the first electrode210. The first electrode 210 is formed so as to become an anode of thelight emitting element 216. Note that the first electrode 210 is formedby a conductive material having light transmittance.

[0121] An organic compound layer 212 is formed on the first electrode210 (anode), and a second electrode (cathode) 213 is formed on theorganic compound layer 212, thereby forming a light emitting element216.

[0122] A structure is taken in Embodiment Mode 1 in which a transparentconductive film which becomes the anode is used in the first electrode210, and therefore light generated by carrier recombination in theorganic compound layer 212 is emitted from the first electrode 210 side.Note that it is preferable that the second electrode 213 is formed by amaterial having light blocking property.

[0123] Note that light passing through from the first electrode 210 sidepasses through the substrate 201 and is released to the outside inEmbodiment Mode 1. It is therefore necessary to use a material havinglight transmittance as the substrate 201, and specifically, glass,quartz, or plastic materials are used.

[0124] [Embodiment Mode 2]

[0125] The following describe a sectional structure of a pixel portionof a light emitting device as Embodiment Mode 2 of the presentinvention, referring to FIG. 2B. The structure is formed is the same asin Embodiment Mode 1 except that the current-controlling TFT 222 isformed by an n-channel type. Thus, the structure formed after that thewiring 209 is formed is described.

[0126] On the first interlayer insulating film 208 is formed a firstelectrode 231 connected electrically to the source region or the drainregion of the current-controlling TFT 222 by the wiring 209. InEmbodiment Mode 2, the first electrode 231 is formed to be a cathode.

[0127] The organic compound layer 233 is formed on the first electrode231, therefore, it is allowable to form a barrier layer 234 by asputtering for preventing the damage of the organic compound layer 233when the second electrode 235 is formed. For the barrier layer 234,copper phthalocyanine (Cu—Pc), gold, platinum or the like may be used.

[0128] Further, the second electrode 235 that is made of a transparentconductive film and that is to be an anode is formed on the barrierlayer 234 can be formed.

[0129] As described above, a light emitting element made of the firstelectrode 231, the organic compound layer 233, the barrier layer 234,and the second electrode 235.

[0130] In the present Embodiment Mode 2, by using a transparentconductive film to be an anode for the second electrode 235, lightgenerated by recombination of carriers in the organic compound layer 233can be emitted from the side of the second electrode 235. The structureis an upward emission structure. In the present Embodiment Mode 2, it ispreferable to use a transparent material to form the first electrode231.

[0131] [Embodiment Mode 3]

[0132] The following describe a sectional structure of a pixel portionof a light emitting device as Embodiment Mode 3 of the present inventionwith reference to FIG. 2C. The current-controlling TFT 222 is formed tobe a p-channel type as same as in the Embodiment Mode 1. Thus, thestructure formed after that the wiring 209 is formed is described.

[0133] On the first interlayer insulating film 208 is formed a firstelectrode 241 connected electrically to the source region or the drainregion of the current-controlling TFT 222 by the wiring 209. InEmbodiment Mode 3, the first electrode 241 is formed to be an anode. Forforming the first electrode 241, a material having a large work functionand functioning as an anode is used. Further, conductive materialshaving light-shielding effect and a high reflectivity are used to formthe first electrode 241.

[0134] An organic compound layer 243 is deposited on the first electrode241. A light emitting elements made of the second electrode 244 isformed thereon. In this Embodiment Mode, the second electrode 244 needsto be formed having transparency, thus, the second electrode 244 ispreferably to be formed having a thickness that can transmit light(visible light).

[0135] In Embodiment Mode 3, light is generated from the organiccompound layer 243 because the second electrode 244 has a transparency,and the light emits from the second electrode side 244. The structure isan upward emission structure.

[0136] In the light emitting device formed by Embodiment Modes 1 to 3,an organic compound layer of a light emitting element can be used anorganic compounds as follows.

[0137] The organic compound layer is formed by a single layer or alamination layer selected from a hole injecting layer, a holetransporting layer, an electron transporting layer, an electroninjecting layer, a hole blocking layer, and a light emitting layer.These layers are made of hole injecting material, a hole transportingmaterial, an electron transporting material, an electron injectingmaterial, a hole blocking material, and a light emitting material.Preferable materials are described as follows. However, materials forlight emitting elements of the present invention are not limited to thefollowing.

[0138] Effective hole injecting materials are, within confines oforganic compounds, porphyrin-based compounds, and phthalocyanine(hereafter, H₂Pc) and copper phthalocyanine (hereafter, CuPc) are oftenused. Among polymers, polyvinyl carbazole (hereafter, PVK) is effectiveas well as the aforementioned materials obtained by performing chemicaldoping on conductive high polymers. Examples of these high polymersinclude polyethylene dioxythiophene (hereafter, PEDOT) doped withpolystyrene sulfonic acid (hereafter, PSS), and polyaniline, orpolypyrrole, doped with iodine or other Lewis acid. A high polymer thatis an insulator is also effective in terms of planarization of theanode, and polyimide (hereafter, PI) is often used. Effective materialsare also found among inorganic compounds, and examples thereof include athin film of gold, platinum or like other metals and a very thin film ofaluminum oxide (hereinafter referred to alumina).

[0139] Materials most widely used as the hole transporting material arearomatic amine-based (namely, those with a benzene ring-nitrogen bond)compounds. Of them, particularly widely used are: aforementioned TPD,besides; its derivative, namely,4,4′-bis-[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereafter, (α-NPD).Also used are star burst aromatic amine compounds, including:4,4′,4″-tris (N,N-diphenyl-amino)-triphenyl amine (hereafter, TDATA);and 4,4′,4″-tris [N-(3-methylphenyl)-N-phenyl-amino]-triphenyl amine(hereafter, MTDATA).

[0140] Metal complexes are often used as the electron transportingmaterial. Examples thereof include: metal complexes having quinolineskeleton or benzoquinoline skeleton, such as the aforementioned Alq,tris (4-methyl-8-quinolinolate) aluminum (hereafter, Almq), and bis(10-hydroxybenzo [h]-quinolinate) beryllium (hereafter, Bebq₂); and bis(2-methyl-8-quinolinolate)(4-hydroxy-biphenylil)-aluminum (hereafter,BAlq) that is a mixed ligand complex. The examples also include metalcomplexes having oxazole-based and thiazole-based ligands such as bis[2-(2-hydroxypheyl)-benzooxazolate] zinc (hereafter, Zn(BOX)₂) and bis[2-(2-hydroxypheyl)-benzothiazolate] zinc (hereafter, Zn(BTZ)₂). Othermaterials that are capable of transporting electrons than the metalcomplexes are: oxadiazole derivatives such as2-(4-biphenylyl)5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereafter, PBD)and 1,3-bis [5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-il] benzene(hereafter, OXD-7); triazole derivatives such as5-(4-biphenylyl)-3-(4-tert-butylphenyl)-4-phenyl-1,2,4-triazole(hereafter, TAZ) and5-(4-biphenylyl)-3-(4-tert-butylphenyl)-4-(4-ethylpheyl)-1,2,4-triazole(hereafter, p-EtTAZ); and phenanthroline derivatives such asbathophenanthroline (hereafter, BPhen) and bathocupuroin (hereafter,BCP).

[0141] The electron transporting material given above can be used as theelectron injecting material. Other than those, a very thin film of aninsulator, including alkaline metal halides such as lithium fluoride andalkaline metal oxides such as lithium oxide, is often used. Alkalinemetal complexes such as lithium acetyl acetonate (hereafter, Li(acac))and 8-quinolinolate-lithium (hereafter, Liq) are also effective.

[0142] The following materials; BAlq, OXD-7, TAZ, p-EtTAZ, BPhen, BCPcan be used as the hole blocking material. It is effective to use thesematerials because they have high excitation energy level.

[0143] Materials effective as the light emitting material are variousfluorescent pigments, in addition to the aforementioned metal complexesincluding Alq₃, AlmQ₃, BeBq₃, BAlq, Zn(BOX)₂, and Zn(BTZ)₂. Tripletlight emission materials may also be used and the mainstream thereof arecomplexes with platinum or iridium as central metal. Known triplet lightemission materials include tris (2-phenylpyridine) iridium (hereafter,Ir(ppy)₃) and 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphyrin-platinum(hereafter, PtOEP).

[0144] Also, although this embodiment is explained by exemplifying atop-gate TFT as a light emitting device formed by Embodiment Modes 1 to3, the invention is not limited to a top-gate TFT, i.e. applicable to abottom-gate TFT, forward-stagger TFT, or another TFT structure.

Embodiments

[0145] Embodiments of the present invention are explained below.

[0146] [Embodiment 1]

[0147] Detailed description will be made of light emitting deviceshaving the element structures explained in Embodiment Mode 1, EmbodimentMode 2, and Embodiment Mode 3, respectively.

[0148]FIG. 3A is a diagram showing an element structure of the lightemitting device disclosed in Embodiment Mode 1. That is, the firstelectrode 210 which is electrically connected to the electric currentcontrol TFT 222, as shown in FIG. 2A, is an anode 301 in FIG. 3A. Anorganic compound layer 302 is formed on the anode 301, and a cathode 308is formed on the organic compound layer 302. Thus, a bottom emissiontype element structure is employed, in which light developed in theorganic compound layer 302 is emitted to the outside through the anode301.

[0149] Note that a conductive film having a large work function andhaving light transmittance, such as ITO or IZO, is used as a materialfor forming the anode 301. The anode 301 is formed at a thickness of 110nm by using ITO in Embodiment 1.

[0150] The organic compound layer 302 is formed next on the anode 301,and the organic compound layer 302 has a laminate structure composed ofa hole injecting layer 303, a hole transporting layer 304, a lightemitting layer 305, a hole blocking layer 306, and an electrontransporting layer 307. Note that although a case of forming the organiccompound layer 302 by using low molecular weight organic compounds isexplained in Embodiment 1, it is also possible to form the organiccompound layer 302 by a single layer, or a laminate, of high molecularweight organic compounds.

[0151] The hole injecting layer 303 is formed at a thickness of 20 nmusing Cu—Pc in Embodiment 1, the hole transporting layer 304 is formedat a thickness of 20 nm using m-MTDATA, the light emitting layer 305 isformed at a thickness of 20 nm using CBP and Ir(ppy)₃, the hole blockinglayer 306 is formed at a thickness of 10 nm using BCP, and the electrontransporting layer 307 is formed at a thickness of 40 nm using Alq₃.

[0152] The cathode 308 is formed next. Note that it is preferable to usea material having light blocking property, having a high reflectivity,and having a small work function as the cathode 308 with the structureshown in FIG. 3A, and therefore an Mg:Ag alloy is used as the cathodematerial, and is formed at a thickness of 120 nm. Note that a laminateof an element residing in Group 1 or Group 2 of the periodic table witha conductive material such as Al, Ti, or W can also be used as thecathode material. In addition, it is also possible to use an alloy ofboth. The bottom emission type light emitting element disclosed inEmbodiment Mode 1 can thus be obtained.

[0153] An element structure of a light emitting device disclosed inEmbodiment Mode 2 is shown in FIG. 3B. That is, the first electrode 231,which is electrically connected to the electric current control TFT 222,as shown in FIG. 2B, is a cathode 311 in FIG. 3B. An organic compoundlayer 312 is formed on the cathode 311, and a barrier layer 318 isformed on the organic compound layer 312, and a cathode 319 is formed onthe barrier layer 318. Thus, a top emission type element structure isadopted in which light developed in the organic compound layer 312passes through the anode 319 and is emitted to the outside.

[0154] Note that, with this element structure, the anode 319 is formedon the organic compound layer 312, but the anode 319 forms ITO, atransparent conductive film by sputtering, and therefore the barrierlayer 306 is formed in order to prevent damage to the organic compoundlayer 303 during sputtering. Note that the barrier layer 306 is mainlyformed using materials formed by evaporation.

[0155] It is preferable to form the anode 311 using a material havinglight blocking property and having high reflectivity, and therefore thecathode 311 is formed having a thickness of 120 nm using Mg:Ag as thecathode material.

[0156] The organic compound layer 312 is formed next on the cathode 311.Materials used in forming the organic compound layer 312 are similar tothose shown by FIG. 3A, but the order of lamination is reversed. Anelectron transporting layer 313, a hole clocking layer 314, a lightemitting layer 315, a hole transporting layer 316, and a hole injectinglayer 317 are laminated in order from the cathode 311 side, forming theorganic compound layer 312. Note that the layers can be formed at thesame thickness as used in FIG. 3A.

[0157] The barrier layer 318 is formed next on the organic compoundlayer 312. Note that the barrier layer 318 is formed between the organiccompound layer 312 and the anode 319, and therefore in addition tomaterials having a large work function such as gold and silver, Cu—Pcand the like can also be used. It is necessary that the barrier layer318 have light transmittance for the case of the structure shown in FIG.3B because light developing in the organic compound layer 312 is emittedto the outside through the barrier layer 318 and the anode 319. InEmbodiment 1, the barrier layer 318 is formed by evaporation using Au ata thickness of 20 nm, one in which the barrier layer has atransmittivity on the order capable of transmitting light. However, forthe case of the structure shown in FIG. 3B, Cu—Pc may be used in thehole injecting layer 317, and Cu—Pc may be applied as the material usedfor forming the barrier layer, thus making the hole injecting layer 317also function as a barrier layer. The barrier layer 318 therefore doesnot always need to be formed.

[0158] The cathode 319 is then formed on the barrier layer 318. Notethat the cathode 319 is formed using a conductive film having lighttransmittance and having a large work function, such as ITO or IZO. Theanode 319 is formed from ITO at a thickness of 110 nm in Embodiment 1.The bottom emission type light emitting element disclosed in EmbodimentMode 2 can thus be obtained.

[0159] An element structure of a light emitting device disclosed inEmbodiment Mode 3 is shown in FIG. 4. That is, the first electrode 241,which is electrically connected to the electric current control TFT 222,as shown in FIG. 2C, is an anode 401 of FIG. 4. An organic compoundlayer 402 is formed on the anode 401, and a cathode 408 is formed on theorganic compound layer 402. Light developed in the organic compoundlayer 402 passes through the cathode 408 and is emitted to the outside,thus forming a top emission type element structure.

[0160] Note that a material having light blocking property, having highreflectivity, and having a large work function is used as the materialfor forming the anode 401. The anode 401 is formed at a thickness of 110nm using tungsten (W) in Embodiment 1.

[0161] The organic compound layer 402 is formed next on the anode 401.The organic compound layer 402 is laminated and formed using materialssimilar to that shown by FIG. 3A, and at the similar film thickness.

[0162] The cathode 408 is formed next on the organic compound layer 402.Note that it is preferable to use a material having light transmittanceand having a small work function for the cathode 408 with the structureshown in FIG. 4, and therefore a laminate of cesium (Cs), residing inGroup 1 of the periodic table, and high conductivity silver (Ag) is usedas the cathode material, and is formed at a film thickness on the orderof 20 nm. Note that light developed in the organic compound layer 402 isreleased to the outside after passing through the cathode 408, andtherefore it is necessary that the cathode have light transmittance. Csis formed contacting the organic compound layer 402 based uponconsidering transmittivity in accordance with the film thickness of thematerials forming the cathode 408, and in addition Ag is formed, makinga laminate structure. Thus, the cathode 408 is formed.

[0163] Note that measurement results relating to the transmittivity oflight when forming the cathode from an extremely thin film are shown inFIG. 13. In FIG. 13, light emitting elements are formed by changing thefilm thickness of the extremely thin film forming the cathode, and thetransmittivity is measured.

[0164] The light emitting elements used here are for cases in which: thecathode is formed by using only 2 nm of cesium; the cathode is formed byusing only 10 nm of silver; and the cathode is formed by laminatingsilver having a film thickness of 5 nm, 10 nm, or 20 nm on a cesium filmformed at a thickness of 2 nm.

[0165] A state in which the film thickness reduces the transmittivitycan be seen. Further, not only transmittivity, but also film resistanceis very important, in order to use the films as second electrodes. Ifthe resistance is high, then the materials cannot be used as electrodematerials even if they have high transmittivity.

[0166] When the sheet resistance of these films was measured, and thelaminate film of 2 nm of cesium and 10 nm of silver was measured at 218Ω/□, and the laminate film of 2 nm of cesium and 20 nm of silver wasmeasured at 13.4 Ω/□. The other films could not be measured.

[0167] Note that the average transmittivity for the cases in which 10 nmof silver and 20 nm of silver are laminated with respect to 2 nm ofcesium is 56% for the former, and 54% for the latter. The averagetransmittivity as used here is the average value obtained when measuringthe transmittivity at various wavelengths form 300 to 800 nm.

[0168] As is understood from the above results, by forming cesium andsilver into a film thickness of from 2 nm and 20 nm, respectively, inEmbodiment 1, an electrode can be formed having not only transmittivity,but having low film resistivity on the order capable of being used as acathode. The cathode 408 is therefore formed by laminating 2 nm ofcesium with 20 nm of silver in Embodiment 1, and the top emission typelight emitting element disclosed in Embodiment Mode 3 can thus beobtained.

[0169] Note that cases of using only cesium elements are explained inEmbodiment 1, but compounds such as cesium fluorides can also be used.These compounds may also be formed at a film thickness of several nm,similar to when only cesium elements are used.

[0170] [Embodiment 2]

[0171] In this embodiment, a method of simultaneously forming, on thesame substrate, a pixel portion and TFTs (n-channel TFT and p-channelTFT) of a driver circuit formed in the periphery of the pixel portionand forming a light emitting element which connect to the TFT at pixelportion is described in detail using FIGS. 5 to 8. Note that, in thisembodiment, light emitting element having the structure described inEmbodiment Mode 1 is formed.

[0172] First, in this example, a substrate 600 is used, which is madefrom glass, such as barium borosilicate glass or aluminum borosilicate,represented by such as Corning #7059 glass and #1737. There is nolimitation on the substrate 600 as long as a substrate having a lighttransparency is used, and a quartz substrate may also be used. A plasticsubstrate having heat resistance to a process temperature of thisembodiment may also be used.

[0173] Then, a base film 601 formed from an insulating film such as asilicon oxide film, a silicon nitride film or a silicon oxynitride film.In this embodiment, a two-layer structure is used as the base film 601.However, a single-layer film or a lamination structure consisting of twoor more layers of the insulating film may be used. As a first layer ofthe base film 601, a silicon oxynitride film 601 a is formed into athickness of 10 to 200 nm (preferably 50 to 100 nm) using SiH₄, NH₃, andN₂O as reaction gases by plasma CVD. In this embodiment, the siliconoxynitride film 601 a (composition ratio Si=32%, O=27%, N=24% and H=17%)having a film thickness of 50 nm is formed.

[0174] Then, as a second layer of the base film 601, a siliconoxynitride film 601 b is formed so as to laminate thereon into athickness of 50 to 200 nm (preferably 100 to 150 nm) using SiH₄ and N₂Oas reaction gases by plasma CVD. In this embodiment, the siliconoxynitride film 601 b (composition ratio Si=32%, O=59%, N=7% and H=2%)having a film thickness of 100 nm is formed.

[0175] Subsequently, semiconductor layers 602 to 605 are formed on thebase film 601. The semiconductor layers 602 to 605 are formed from asemiconductor film having an amorphous structure by a known method (asputtering method, an LPCVD method, or a plasma CVD method), and issubjected to a known crystallization process (a laser crystallizationmethod, a thermal crystallization method, or a thermal crystallizationmethod using a catalyst such as nickel). The crystalline semiconductorfilm thus obtained is patterned into desired shapes to obtain thesemiconductor layers. The semiconductor layers 602 to 605 are formedinto the thickness of from 25 to 80 nm (preferably 30 to 60 nm). Thematerial of the crystalline semiconductor film is not particularlylimited, but it is preferable to form the film using silicon, a silicongermanium (Si_(1-x)Ge_(x)(x=0.0001 to 0.02)) alloy, or the like.

[0176] In this embodiment, 55 nm thick amorphous silicon film is formedby plasma CVD, and then, nickel-containing solution is held on theamorphous silicon film. A dehydrogenating process of the amorphoussilicon film is performed (500° C. for one hour), and thereafter athermal crystallization process is performed (550° C. for four hours)thereto. Further, to improve the crystallinity thereof, laser annealtreatment is performed to form the crystalline silicon film. Then, thiscrystalline silicon film is subjected to a patterning process using aphotolithography method, to obtain the semiconductor layers 602 to 605.

[0177] Further, before or after the formation of the semiconductorlayers 602 to 605, a minute amount of impurity element (boron orphosphorus) may be doped to control a threshold value of the TFT.

[0178] Besides, in the case where the crystalline semiconductor film ismanufactured by the laser crystallization method, a pulse oscillationtype or continuous-wave type gas state laser or solid state laser. Asthe gas sate laser, excimer laser, Ar laser, or Kr laser may be used. Asthe solid state laser, YAG laser, YVO₄ laser, YLF laser, YalO₃ laser,glass laser, ruby laser, alexandrite laser, Ti: sapphire laser may beused.

[0179] In the case where those lasers are used, it is appropriate to usea method in which laser light radiated from a laser oscillator iscondensed by an optical system into a linear beam, and is irradiated tothe semiconductor film. Although the conditions of the crystallizationshould be properly selected by an operator, in the case where theexciter laser is used, a pulse oscillation frequency is set as 300 Hz,and a laser energy density is as 100 to 400 mJ/cm² (typically 200 to 300mJ/cm²). In the case where the YAG laser is used, it is appropriate thatthe second harmonic is used to set a pulse oscillation frequency as 30to 300 kHz, and a laser energy density is set as 300 to 600 mJ/cm²(typically, 350 to 500 mJ/cm²). Then, laser light condensed into alinear shape with a width of 100 to 1000 μm, for example, 400 μm isirradiated to the whole surface of the substrate, and an overlappingratio (overlap ratio) of the linear laser light at this time may be setas 50 to 90%.

[0180] A gate insulating film 607 is then formed for covering thesemiconductor layers 602 to 605. The gate insulating film 607 is formedfrom an insulating film containing silicon by plasma CVD or sputteringinto a film thickness of from 40 to 150 nm. In the embodiment, the gateinsulating film 607 is formed from a silicon oxynitride film into athickness of 110 nm by plasma CVD (composition ratio Si=32%, O=59%,N=7%, and H=2%). Of course, the gate insulating film 607 is not limitedto the silicon oxynitride film, an insulating film containing othersilicon may be formed into a single layer of a lamination structure.

[0181] Beside, when the silicon oxide film is used, it can be formed byplasma CVD in which TEOS (tetraethyl orthosilicate) and O₂ are mixed,with a reaction pressure of 40 Pa, a substrate temperature of from 300to 400° C., and discharged at a high frequency (13.56 MHz) power densityof 0.5 to 0.8 W/cm². Good characteristics as the gate insulating filmcan be obtained in the silicon oxide film thus manufactured bysubsequent thermal annealing at 400 to 500° C.

[0182] Then, as shown in FIG. 5A, on the gate insulating film 607, afirst conductive film 608 and a second conductive film 609 are formedinto lamination to have a film thickness of 20 to 100 nm and 100 to 400nm, respectively. In this embodiment, the first conductive film 608 madefrom a TaN film with a film thickness of 30 nm and the second conductivefilm 609 made from a W film with a film thickness of 370 nm are formedinto lamination. The TaN film is formed by sputtering with a Ta targetunder an atmosphere containing nitrogen. Besides, the W film is formedby the sputtering method with a W target. The W film may be formed bythermal CVD using tungsten hexafluoride (WF₆).

[0183] Whichever method is used, it is necessary to make the materialhave low resistance for use as the gate electrode, and it is preferredthat the resistivity of the W film is set to less than or equal to 20μΩcm. By making the crystal grains large, it is possible to make the Wfilm have lower resistivity. However, in the case where many impurityelements such as oxygen are contained within the W film, crystallizationis inhibited and the resistance becomes higher. Therefore, in thisembodiment, by forming the W film having high purity by sputtering usinga target having a purity of 99.9999%, and in addition, by takingsufficient consideration to prevent impurities within the gas phase frommixing therein during the film formation, a resistivity of from 9 to 20μΩcm can be realized.

[0184] Note that, in this embodiment, the first conductive film 608 ismade of TaN, and the second conductive film 609 is made of W, but thematerial is not particularly limited thereto, and either film may beformed of an element selected from Ta, W, Ti, Mo, Al, Cu, Cr and Nd oran alloy material or a compound material containing the above element asits main ingredient. Besides, a semiconductor film typified by apolycrystalline silicon film doped with an impurity element such asphosphorus may be used. Also, an alloy containing Ag, Pd, Cu can beused.

[0185] Besides, any combination may be employed such as a combination inwhich the first conductive film 608 is formed of tantalum (Ta) and thesecond conductive film 609 is formed of W, a combination in which thefirst conductive film 608 is formed of titanium nitride (TiN) and thesecond conductive film 609 is formed of W, a combination in which thefirst conductive film 608 is formed of tantalum nitride (TaN) and thesecond conductive film 609 is formed of Al, or a combination in whichthe first conductive film 608 is formed of tantalum nitride (TaN) andthe second conductive film 609 is formed of Cu, or a combination inwhich the first conductive film 608 is formed of W, Mo, or thecombination of W and Mo and the second conductive film 609 is formed ofAl and Si or Al and Ti or Al and Sc or Al and Nd, further, the thirdconductive film (not shown) is formed from Ti, TiN or the combination ofTi and TiN.

[0186] Next, masks 610 to 613 made of resist are formed using aphotolithography method, and a first etching process is performed inorder to form electrodes and wirings as shown in FIG. 5B. This firstetching process is performed with the first and second etchingconditions. In this embodiment, as the first etching conditions, an ICP(inductively coupled plasma) etching method is used, a gas mixture ofCF₄, Cl₂ and O₂ is used as an etching gas, the gas flow rate is set to25/25/10 scem, and plasma is generated by applying a 500 W RF (13.56MHz) power to a coil shape electrode under 1 Pa. A dry etching devicewith ICP (Model E645-□ICP) produced by Matsushita Electric IndustrialCo. Ltd. is used here. A 150 W RF (13.56 MHz) power is also applied tothe substrate side (test piece stage) to effectively apply a negativeself-bias voltage.

[0187] The W film is etched with the first etching conditions, and theend portion of the first conductive layer is formed into a taperedshape. In the first etching conditions, the etching rate for W is 200.39nm/min, the etching rate for TaN is 80.32 nm/min, and the selectivity ofW to TaN is about 2.5. Further, the taper angle of W is about 26° withthe first etching conditions.

[0188] Thereafter, as shown in FIG. 5B, the first etching conditions arechanged into the second etching conditions without removing the masks610 to 613 made of resist, a mixed gas of CF₄ and Cl₂ is used as anetching gas, the gas flow rate is set to 30/30 scem, and plasma isgenerated by applying a 500 W RF (13.56 MHz) power to a coil shapeelectrode under 1 Pa to thereby perform etching for about 15 seconds. A20 W RF (13.56 MHz) power is also applied to the substrate side (testpiece stage) to effectively a negative self-bias voltage. The W film andthe TaN film are both etched on the same order with the second etchingconditions in which CF₄ and Cl₂ are mixed.

[0189] In the second etching conditions, the etching rate for W is 58.97nm/min, and the etching rate for TaN is 66.43 nm/min. Note that, theetching time may be increased by approximately 10 to 20% in order toperform etching without any residue on the gate insulating film.

[0190] In the first etching process, the end portions of the first andsecond conductive layers are formed to have a tapered shape due to theeffect of the bias voltage applied to the substrate side by adoptingmasks of resist with a suitable shape. The angle of the tapered portionsmay be set to 15° to 45°. Thus, first shape conductive layers 615 to 618(first conductive layers 615 a to 618 a and second conductive layers 615b to 618 b) constituted of the first conductive layers and the secondconductive layers are formed by the first etching process. Referencenumeral 620 denotes a gate insulating film, and regions of the gateinsulating film which are not covered by the first shape conductivelayers 615 to 618 are made thinner by approximately 20 to 50 nm byetching.

[0191] Then, a first doping process is performed to add an impurityelement for imparting an n-type conductivity to the semiconductor layerwithout removing the mask made of resist (FIG. 5B). Doping may becarried out by an ion doping method or an ion injecting method. Thecondition of the ion doping method is that a dosage is 1×10¹³ to 5×10¹⁵atoms/cm², and an acceleration voltage is 60 to 100 keV. In thisembodiment, the dosage is 1.5×10¹⁵ atoms/cm² and the accelerationvoltage is 80 keV.

[0192] As the impurity element for imparting the n-type conductivity, anelement which belongs to Group 15 of the periodic table, typicallyphosphorus (P) or arsenic (As) is used, and phosphorus is used here. Inthis case, the conductive layers 615 to 618 become masks to the impurityelement for imparting the n-type conductivity, and high concentrationimpurity regions 621 to 624 are formed in a self-aligning manner. Theimpurity element for imparting the n-type conductivity is added to thehigh concentration impurity regions 621 to 624 in the concentrationrange of 1×10²⁰ to 1×10²¹ atoms/cm³.

[0193] Thereafter, the second etching process is performed withoutremoving the masks made of resist as shown in FIG. 5C. The secondetching process is performed by third or fourth etching condition. Here,a mixed gas of CF₄, Cl₂ is used as an etching gas, the gas flow rate isset to 30/30 sccm, and plasma is generated by applying a 500 W RF (13.56MHz) power to a coil shape electrode under 1 Pa to thereby performetching for about 60 seconds. A 20 W RF (13.56 MHz) power is alsoapplied to the substrate side (test piece stage) to effectively apply anegative self-bias voltage. The W film and the TaN film are both etchedon the same order with the third etching conditions in which CF₄ and Cl₂are mixed.

[0194] In the second etching process, the etching rate for W is 58.97nm/min, the etching rate for TaN is 66.43. Note that, the etching timemay be increased by approximately 10 to 20% in order to perform etchingwithout any residue on the gate insulating film.

[0195] Thereafter, as shown in FIG. 5C, the third etching conditions arechanged into the fourth etching conditions. Without removing the masks610 to 613 made of resist, a mixed gas of CF₄, Cl₂ and O₂ is used as anetching gas, the gas flow rate is set to 20/20/20 seem, and plasma isgenerated by applying a 500 W RF (13.56 MHz) power to a coil shapeelectrode under 1 Pa to thereby perform etching for about 20 seconds. A20 W RF (13.56 MHz) power is also applied to the substrate side (testpiece stage) to effectively apply a negative self-bias voltage.

[0196] In the fourth etching conditions, etching rate for TaN is 14.83nm/min. Therefore, the W film etched selectively. According to thefourth etching process, the second conductive layers 626 to 629 (firstconductive layer 626 a to 629 a and second conductive layers 626 b to629 b) are formed.

[0197] Next, a second doping process is performed as shown in FIG. 6A.Second conductive layers 626 b to 629 b are used as masks to an impurityelement, and doping is performed such that the impurity element is addedto the semiconductor layer below the tapered portions of the firstconductive layers. In this embodiment, phosphorus (P) is used as theimpurity element, and plasma doping is performed with the dosage of1.5×10¹⁴ atoms/cm², current density of 0.5 μA and the accelerationvoltage of 90 keV.

[0198] Thus, low concentration impurity regions 631 a to 634 a, whichoverlap with the first conductive layers and low concentration impurityregions 631 b to 634 b, which do not overlap with the first conductivelayers are formed in a self-aligning manner. The concentration ofphosphorus (P) in the low concentration impurity regions 631 to 634 is1×10¹⁷ to 5×10¹⁸ atoms/cm³. Further, the impurity element is added tothe high concentration impurity regions 621 to 624 and the highconcentration impurity regions 635 to 638 are formed.

[0199] New masks are formed from resist (639 and 640), and a thirddoping process is performed as shown in FIG. 6B. Impurity regions 641 to642, to which an impurity element is added that imparts the oppositeconductivity type (p-type) from the single conductivity type (n-type)are formed to the semiconductor layers, which become active layers ofp-channel TFTs, by the third doping process. The first conductive layers627 a and the second conductive layer 627 b are used as masks againstthe impurity element, the impurity element imparting p-type conductivityis added, and the impurity regions are formed in a self-aligning manner.

[0200] The impurity regions 641 to 642 are formed in Embodiment 2 by iondoping using diborane (B₂H₆). Phosphorous is added to the impurityregions 641 to 642 in differing concentrations, respectively, by thefirst doping process and by the second doping process. However, dopingis performed such that the concentration of the impurity element whichimparts p-type conductivity to each of the regions becomes from 2×10²⁰to 2×10²¹ atoms/cm³, and therefore no problems will develop with theregions functioning as source regions and drain regions of p-channelTFTs.

[0201] The resist masks 639 and 640 are removed next, and a firstinterlayer insulating film 643 is formed as shown in FIG. 6C. In thisembodiment, as the first inter layer insulating film 643, the laminationfilm is formed from the first insulating film 643 a containing siliconand nitride and the second insulating film 643 b containing silicon andoxygen.

[0202] An insulting film containing silicon is formed having a thicknessof 100 to 200 nm, using plasma CVD or sputtering, as the firstinterlayer insulating film 643 a. A silicon oxynitride film is formedwith a film thickness of 100 nm by plasma CVD in Embodiment 2. The firstinterlayer insulating film 643 a is of course not limited to the siliconoxynitride film, and other insulating films containing silicon may beused in a single layer or a lamination structure.

[0203] Next, a process for activating the impurity elements added toeach of the semiconductor layers is performed. Thermal annealing usingan annealing furnace is performed for the activation process. Thermalannealing may be performed in a nitrogen atmosphere having an oxygenconcentration of 1 ppm or less, preferably 0.1 ppm or less, at 400 to700° C., typically between 500 and 550° C. The activation process isperformed in Embodiment 2 by heat treatment at 550° C. for four hours.Note that, in addition to thermal annealing, laser annealing and rapidthermal annealing (RTA) can also be applied.

[0204] Note also that, in Embodiment 2, nickel used as a catalyst duringcrystallization is gettered into the impurity regions 635, 637, and 638containing phosphorous at a high concentration at the same time as theabove activation process is performed. The nickel concentration withinthe semiconductor layers that mainly become channel forming regions isthus reduced. The value of the off current is reduced for TFIs havingchannel forming regions thus formed, and a high electric field effectmobility is obtained because of the good crystallinity. Thus, goodproperties can be achieved.

[0205] Further, the activation process may also be performed beforeforming the first interlayer insulating film. However, when using awiring material which is weak with respect to heat, it is preferable toperform the activation process after forming the interlayer insulatingfilm (insulating film containing silicon as its main constituent,silicon nitride film, for example) in order to protect the wirings andthe like, as in Embodiment 2.

[0206] The doping process may be performed, and the first interlayerinsulating film may be formed after performing the activation process.

[0207] In addition, heat treatment is performed for 1 to 12 hours at 300to 550° C. in an atmosphere containing hydrogen of 3 to 100%, performinghydrogenation of the semiconductor layers. Heat treatment is performedfor one hour at 410° C. in a atmosphere containing approximately 3%hydrogen in Embodiment 2. This process is one for terminating danglingbonds of the semiconductor layers by hydrogen contained in theinterlayer insulating film. Plasma hydrogenation (using hydrogen excitedby plasma) may be performed as another means of hydrogenation.

[0208] Further, when using a laser annealing method as the activationprocess, it is preferable to irradiate laser light such as that from anexcimer laser or a YAG laser after performing the above hydrogenationprocess.

[0209] A second interlayer insulating film 643 b is formed next on thefirst interlayer insulating film 643 a from insulating film containingsilicon with a thickness of 1 to 2 μm by plasma CVD or sputtering. Anoxynitride film having a film thickness of 1.2 μm is formed inEmbodiment 2. Of course, the second insulating film 643 b is not limitedto the above mentioned film, an insulating film containing other siliconmay be formed into a single layer or a lamination structure.

[0210] Then the first interlayer insulating film 643 made from firstinsulating film 643 a and second insulating film 643 b can be formed.

[0211] Next, patterning is performed in order to form contact holes forreaching the impurity regions 635, 636, 637, and 638.

[0212] In addition, the first insulating film 643 a and the secondinsulating film 643 b are insulating film contained silicon formedplasma CVD, so that dry etching method or wet etching method can be usedfor forming a contact hole. However, in this embodiment, wet etchingmethod is used for etching the first insulating film, and the dryetching method is used for etching the second insulating film.

[0213] First, the second insulating film 643 b is etched. Here, a mixedsolution (Stella chemifa Inc., brand name LAL 500) contained 7.13% ofhydrogen ammonium fluoride (NH₄HF₂) and 15.4% of ammonium fluoride(NH₄F) is used as a etchant to conduct a wet etching at 20° C.

[0214] Next, the first insulating film 643 a is etched. CHF₄ is used asan etching gas, and gas flow rates are set to 35 sccm. An 800 W RFelectric power is applied at a pressure of 7.3 Pa, and dry etching isperformed.

[0215] Wirings 645 to 651 are formed that connect electrically with highconcentration impurity regions 635, 636, 637, and 638 respectively. Inthis embodiment, these wirings are formed by patterning Al film in 500nm thicknesses. Besides, a single layer constituted Ti, TiN, Al: Si andthe like, or a lamination layer laminated Ti, TiN, Al: Si, and Ti inturn can also be used. (FIG. 7A) Further, the conductive material 653 tobe a cathode is formed so as to contact with the wiring 652. Theconductive material 653 is formed by being deposited in 110 nm inthickness and patterned using Mg:Ag as a cathode material.

[0216] The insulating film 654 is formed in 1 μm thickness on theconductive material 653. (FIG. 7B) As material forming an insulatingfilm, a film containing silicon oxide is used in this embodiment.Another films such as insulating film containing silicon nitride, orsilicon oxide nitride, the organic resin film, polyimide, polyamide,acrylic (photosensitive acrylic is included), BCB (benzocyclobutene), orthe like may also be used.

[0217] The insulator 654 and the conductive material 653 is polished byusing CMP method. Here, ammonia solution dispersed silica is used asslurry. The process by another CMP method is omitted the descriptionbecause it is described in FIGS. 1A to 1C. With the process, a cathode655 and a planarized insulating film 656 are formed as shown in FIG. 7C,and thus flat faces by these are formed.

[0218] As shown in FIG. 8A, an organic compound layer 657 is formed byan evaporation method on the cathode 655. For the materials to form theorganic compound layer, combination materials shown in Embodiment Modescan be used.

[0219] Next, an anode 658 is formed covering the organic compound layer657 and the planarized insulating film 656 as shown in FIG. 8B. In thisembodiment, as a material of forming the anode 658, an indium-tin oxide(ITO) film is used. When a transparent conductive film have a large workfunction, another known materials can be used to form the anode 658.

[0220] As shown in FIG. 8B, an element substrate having a light emittingelement 659 that is composed of the cathode 655 connected to the currentcontrol TFT 704 electrically, the planarized insulating film 656 formedbetween the cathode 655 and the cathode included in next pixel, theorganic conductive layer 657 formed on the cathode 655, and the anode658 formed on the organic compound layer 657 and the planarizedinsulating film 656 can be formed.

[0221] Note that, in the process of manufacturing the light emittingdevice in this embodiment, although the source signal lines are formedby materials which form the gate electrodes, and although the gatesignal lines are formed by wiring materials which forms the source anddrain electrodes, with relation to the circuit structure and process,other materials may also be used.

[0222] Further, a driver circuit 705 having an n-channel TFT 701 and ap-channel TFT 702, and a pixel portion 706 having a switching TFT 703and a current control TFT 704 can be formed on the same substrate.

[0223] The n-channel TFT 701 of the driver circuit 705 has the channelforming region 501, the low concentration impurity region 631 a (GOLDregion) which overlaps with the first conductive layer 626 a forming aportion of the gate electrode, the low concentration impurity region 631b (LDD region) which does not overlaps with the first conductive layer626 a, and the high concentration impurity region 635 which functions asa source region or a drain region. The p-channel TFT 702 has the channelforming region 502, and the impurity regions 641 and 642 that functionas source regions or drain regions.

[0224] The switching TFT 703 of the pixel portion 706 has the channelforming region 503, the low concentration impurity region 633 a (GOLDregion) which overlap with the first conductive layer 628 a, the lowconcentration impurity region 633 b (LDD region) which does not overlapwith the first conductive layer 628 a, and the high concentrationimpurity region 637 which functions as a source region or a drainregion.

[0225] The current control TFT 704 of the pixel portion 706 has thechannel forming region 504, the low concentration impurity region 634 a(GOLD region) which overlap with the first conductive layer 629 a, thelow concentration impurity region 634 b (LDD region) which does notoverlap with the first conductive layer 628 a, and the highconcentration impurity region 638 which function as source regions ordrain regions.

[0226] In this embodiment, the driving voltage of a TFT is 1.2 to 10 V,preferably 2.5 to 5.5 V.

[0227] When the display of the pixel portion is active (case of themoving picture display), a background is displayed by pixels in whichthe light emitting elements emit light and a character is displayed bypixels in which the light emitting elements do not emit light. However,in the case where the moving picture display of the pixel portion isstill for a certain period or more (referred to as a standby time in thepresent specification), for the purpose of saving electric power, it isappropriate that a display method is changed (inverted). Specifically, acharacter is displayed by pixels in which light emitting elements emitlight (also called a character display), and a background is displayedby pixels in which light emitting elements do not emit light (alsocalled a background display).

[0228] A detailed top surface structure of a pixel portion is shown inFIG. 10A, and a circuit diagram thereof is shown in FIG. 10B. FIGS. 10Aand 10B denoted by a same reference numerals.

[0229] In FIGS. 10A and 10B, a switching TFT 1000 provided on asubstrate is formed by using the switching TFT (n-channel type) TFT 703of FIG. 8B. Therefore, an explanation of the switching (n-channel type)TFT 703 may be referred for an explanation of the structure. Further, awiring indicated by reference numeral 1002 is a gate wiring forelectrically connecting with gate electrodes 1001 (101 a and 1001 b) ofthe switching TFT 1000.

[0230] Note that, in this embodiment, a double gate structure isadopted, in which two channel forming regions are formed, but a singlegate structure, in which one channel forming region is formed, or atriple gate structure, in which three channel forming regions areformed, may also be adopted.

[0231] Further, a source of the switching TFT 1000 is connected to asource wiring 1003, and a drain thereof is connected to a drain wiring1004. The drain wiring 1004 is electrically connected with a gateelectrode 1006 of a current control TFT 1005. Note that the currentcontrol TFT 1005 is formed by using the current control (n-channel type)TFT 704 of FIG. 8B. Therefore, an explanation of the current control(n-channel type) TFT 704 may be referred for an explanation of thestructure. Note that, although the single gate structure is adopted inthis embodiment, the double gate structure or the triple gate structuremay also be adopted.

[0232] Further, a source of the current control TFT 1005 is electricallyconnected with a current supply line 1007, and a drain thereof iselectrically connected with a drain wiring 1008. Besides, the drainwiring 1008 is electrically connected with a cathode 1009 indicated by adotted line.

[0233] A wiring indicated by reference numeral 1010 is a gate wiringconnected with the gate electrode 1012 of the erasing TFT 1011. Further,a source of the erasing TFT 1011 is electrically connected to thecurrent supply line 1007, and a drain thereof is electrically connectedto the drain wiring 1004.

[0234] The erasing TFT 1011 is formed like a current controlling TFT(n-channel type) 704 in FIG. 8B. Therefore, an explanation of thestructure is referred to that of the current controlling TFT (n-channeltype) 704. In this embodiment, a single gate structure is describedthough, a double gate structure or a triple gate structure can be used.

[0235] At this time, a storage capacitor (condenser) is formed in aregion indicated by reference numeral 1013. The capacitor 1013 is formedby a semiconductor film 1014 electrically connected with the currentsupply line 1007, an insulating film (not shown) of the same layer as agate insulating film, and the gate electrode 1006. Further, a capacitorformed by the gate electrode 1006, the same layer (not shown) as a firstinterlayer insulating film, and the current supply line 1007 may be usedas a storage capacitor.

[0236] The light emitting element 1015 shown in circuit diagram in FIG.10B is composed of the cathode 1009, an organic compound layer (notillustrated) formed on the cathode 1009, and an anode (not illustrated)formed on the organic compound layer. In the present invention, thecathode 1009 is connected with a source region and a drain region of thecurrent controlling TFT 1005.

[0237] A counter potential is supplied to the anode of the lightemitting element 1005. In addition, the power source potential issupplied to the power supply line V. A potential difference between thecounter potential and the power source potential is always maintained atsuch a level that causes the light emitting element to emit light whenthe power source potential is applied to the pixel electrode. The powersource potential and the counter potential are supplied to the lightemitting device of the present invention by means of a power sourceprovided by an externally-attached IC chip or the like. In the presentspecification, the power source supplying a counter potential isreferred to as the counter power source 1016.

[0238] [Embodiment 3]

[0239] In this embodiment, the structure of the pixel portion of thelight emitting device that is different from shown in Embodiment 1 isdescribed with reference to FIGS. 9A and 9B.

[0240]FIG. 9A is a top-surface view of the pixel portion that is a pixel907 formed into active matrix shape in the light emitting device havinga driver circuit and a pixel portion.

[0241] Between the pixel portion 907, a source line 905 and a currentsupply line 906 is formed that is electrically connected with the drivercircuit. In this embodiment, between the source line 905 and the currentsupply line 906, an auxiliary electrode 908 made of a conductivematerials is formed.

[0242] In each pixel portion 907 shown in FIG. 9A, a first electrode 909is formed, which is made of conductive film having light shieldingeffect that is to be as an anode of the light emitting element.Specifically, for improving an injection of hole from an anode, it ispreferably to use materials having large work function. As materials forforming the first electrode 909, metal material such as platinum (Pt),chrome (Cr), tungsten (W), or nickel (Ni) can be used.

[0243]FIG. 9B is a cross-sectional view of the top-surface view of FIG.9A taken along the line P-P′. It shows a light emitting device as acomplete state that is formed until the state in FIG. 9A. On the firstelectrode 909 formed in each pixel 907, an organic compound layer 910 isformed. The organic compound layer 910 is formed to cover the firstelectrode 909 completely.

[0244] Next, the second electrode 911 is formed on the organic compoundlayer 910. In this embodiment, the second electrode 911 is formed by atransparent conductive film that is to be a cathode of the lightemitting element. Specifically, for improving an injection of anelectron from a cathode, it is preferably to use materials having smallwork function. The material belonging to an alkaline metal oralkaline-earth metals can be used alone, laminating can be carried outto other material, or the alloy formed with other material can be used.In addition, in this embodiment, second electrode 911 can be formed bylaminating of the aluminum or silver which has the cesium (Cs) which isan alkaline metal, and conductivity.

[0245] In addition, in this embodiment, since second electrode 911 is anelectrode which penetrate the light generated in the light emittingelement, it needs to have transparency. Therefore, the cesium filmformed in contact with the organic compound layer 910 is formed by 2 nmin thick, and the aluminum film or silver film laminated thereof isformed by 20 nm in thick.

[0246] An electrode that has the light transparency can be formed inthis way by forming second electrode 911 that consists of aextremely-thin film.

[0247] In addition, since second electrode 911 formed here is formed incontact with auxiliary electrode 908 formed simultaneously with firstelectrode 909, it can lower film resistance of the second electrode.

[0248] Thus, since the film resistance can be suppressed when the secondelectrode is formed extremely-thin film, in order to secure thetransmittance of the second electrode, driver voltage can be suppressed.

[0249] In addition, in the case of the other element structures shown byEmbodiment Modes 1 and 2, it combines freely, and composition of thiscase of this embodiment can be carried out.

[0250] [Embodiment 4]

[0251] Referring to FIGS. 11, the external appearance of an activematrix type light emitting device of the present invention will bedescribed in Embodiment 4. FIG. 11A is a top view of the light emittingdevice, and FIG. 11B is a sectional view taken on line A-A′ of FIG. 11A.Reference number 1101 represents a source signal line driver circuit,which is shown by a dotted line; 1102, a pixel portion; 1103, a gatesignal line driver circuit; 1104, a cover material; and 1105, a sealant.Inside surrounded by the sealant 1105 is an empty space.

[0252] Reference number 1108 represents wiring for transmitting signalsinputted to the source signal line driver circuit 1101 and the gatesignal line driver circuit 1103. The wiring 1108 receives video signalsor clock signals from a flexible print circuit (FPC) 1109, which will bean external input terminal. Only the FPC is illustrated, but a printedwiring board (PWB) may be attached to this FPC. The light emittingdevice referred to in the present specification may be the body of thelight emitting device, or a product wherein an FPC or a PWB is attachedto the body.

[0253] The following will describe a sectional structure, referring toFIG. 11B. The driver circuits and the pixel portion are formed on thesubstrate 1110, but the source signal line driver circuit 1101 as one ofthe driver circuits and the pixel portion 1102 are shown in FIG. 11B.

[0254] In the source signal line driver circuit 1101, a CMOS circuitwherein an n-channel type TFT 1113 and a p-channel type TFT 1114 arecombined is formed. The TFTs constituting the driver circuit may becomposed of known CMOS circuits, PMOS circuits or NMOS circuits. InEmbodiment 4, a driver-integrated type, wherein the driver circuit isformed on the substrate, is illustrated, but the driver-integrated typemay not necessarily be adopted. The driver may be fitted not to thesubstrate but to the outside.

[0255] The pixel portion 1102 is composed of plural pixels including acurrent-controlling TFT 1111 and an anode 1112 electrically connected tothe drain of the TFT 1111.

[0256] On the both sides of the anode 1112, insulating layer 1113 areformed, and an organic compound layer 1114 formed right on the anode1112. Furthermore, a cathode 1114 is formed on the organic compoundlayer 1114. In this way, a light emitting element 1118 composed of theanode 1112, the organic compound layer 1114 and the cathode 1117 isformed.

[0257] The cathode 1117 also functions as a wiring common to all of thepixels. And the cathode 1117 is electrically connected through theinterconnection line 1108 to the FPC 1109.

[0258] In order to confine the light emitting element 1118 formed on thesubstrate 1110 airtightly, the cover material 1104 is adhered to thesubstrate 1110 with the sealant 1105. A spacer made of a resin film maybe set up to keep a given interval between the cover material 1104 andthe light emitting element 1118. An inert gas such as nitrogen is filledinto the space 1107 inside the sealant 1105. As the sealant 1105, anepoxy resin is preferably used. The sealant 705 is desirably made of amaterial through which water content or oxygen is transmitted asslightly as possible. Furthermore, it is allowable to incorporate amaterial having moisture absorption effect or a material havinganti-oxidation effect into the space 1107.

[0259] In Embodiment 4, as the material making the cover material 1104,there may be used a glass substrate, a quartz substrate, or a plasticsubstrate made of fiber glass-reinforced plastic (FRP), polyvinylfluoride (PVF), mylar, polyester or polyacrylic resin. After theadhesion of the cover material 1105 to the substrate 1110 with thesealant 1105, a sealant is applied so as to cover the side faces(exposure faces).

[0260] As described above, the light emitting element is airtightly putinto the space 1107, so that the light emitting element can becompletely shut out from the outside and materials promotingdeterioration of the organic compound layer, such as water content andoxygen, can be prevented from invading this layer from the outside.Consequently, the light emitting device can be made highly reliable.

[0261] The structure of Embodiment 4 may be freely combined with thestructure of Embodiments 1 to 3.

[0262] [Embodiment 5]

[0263] Embodiments 1 to 4 describes an active matrix type light emittingdevice having a top gate TFT. However, the TFT structure of the presentinvention is not limited thereto and bottom gate TFTs (typically reversestagger TFTs) may also be used in carrying out the present invention asshown in FIG. 12B. The reverse stagger TFTs may be formed by any method.

[0264]FIG. 12A is a top view of a light emitting device that uses bottomgate transistors. Note that the sealing in not conducted yet by sealingsubstrate. A source side driving circuit 1201, a gate side drivingcircuit 1202, and a pixel portion 1203 are formed therein. FIG. 12Bshows in section a region a 1204 of the pixel portion 1203. Thesectional view is obtained by cutting the light emitting device alongthe line x-x′ in FIG. 12A.

[0265]FIG. 12B illustrates only a current controlling TFT out of TFTsthat constituted in a pixel portion 1203. Reference symbol 1211 denotesa substrate and 1212 denotes an insulating film to serve as a base(hereinafter referred to as a base film). A transparent substrate isused for the substrate 1211, typically, a glass substrate, a quartzsubstrate, a glass ceramic substrate, or a crystallized glass substrate.However, the one that can withstand the highest process temperatureduring the manufacture process has to be chosen.

[0266] The base film 1212 is effective especially when a substratecontaining a movable ion or a conductive substrate is used. If a quartzsubstrate is used, the base film may be omitted. An insulating filmcontaining silicon is used for the base film 1212. The term insulatingfilm containing silicon herein refers to an insulating film containingoxygen or nitrogen in a given ratio to the content of silicon,specifically, a silicon oxide film, a silicon nitride film, or a siliconoxynitride film (SiOxNy: x and y are arbitrary integers).

[0267] Reference symbol 1213 denotes a current controlling TFT that is ap-channel transistor. Note that, in this embodiment, cathode 1223 oflight emitting element 1222 is connected the current control transistor1213. Therefore, the cathode 1223 are preferably made from p-channel TFTbut also made from n-channel TFT.

[0268] The current controlling transistor 1213 is composed of an activelayer which comprising source region 1214, drain region 1215 and channelforming region 1216, a gate insulating film 1217, a gate electrode 1218,a interlayer insulating film 1219, a source wiring line 1220, and adrain wiring line 1221. The current controlling transistor 1213 in thisexample is a p-channel transistor.

[0269] The switching TFT has a drain region connected to the gateelectrode 1218 of the current controlling TFT 1213. The gate electrode1218 of the current controlling transistor 1213 is electricallyconnected to the drain region (not shown) of the switching transistorthrough a drain wiring line (not shown), to be exact. The gate electrode1218 has a single gate structure but may take a multi-gate structure.The source wiring line 1220 of the current controlling transistor 1213is connected to a current supplying line (not shown).

[0270] The current controlling TFT 1213 is an element for controllingthe amount of current supplied to the light emitting element 1222, and arelatively large amount of current flows through this TFT. Therefore, itis preferable to design the current controlling TFT to have a channelwidth (W) wider than the channel width of the switching transistor. Itis also preferable to design the current controlling TFT to have arather long channel length (L) in order to avoid excessive current flowin the current controlling TFT 1213. Desirably, the length is set suchthat the current is 0.5 to 2 μA (preferably 1 to 1.5 μA) per pixel.

[0271] If the active layer (channel formation region, in particular) ofthe current controlling transistor 1213 is formed thick (desirably 50 to100 nm, more desirably 60 to 80 nm), degradation of the transistor canbe slowed.

[0272] After the current controlling TFT 1213 is formed, the interlayerinsulating film 1219 is formed and cathode 1223 that is electricallyconnected to the current controlling TFT 1213 is formed. In thisembodiment, the current controlling transistor 1213, the wiring thatconnects the cathode 1223 electrically and cathode 1223 are formed atthe same time and same material. As the materials of cathode 1223, theconductive film having small working function is preferably used. Inthis example, the cathode 1223 formed from Mg:Ag.

[0273] On the anode 1223, the organic compound layer 1226 is formed tocover the cathode 1223, and the anode 1228 is formed thereof. Asmaterial for forming the anode 1228, a transparent conductive filmhaving a transparency is used. In this embodiment, ITO is deposited in110 nm thick, and the anode 1228 is formed. Not illustrated, a barrierlayer can be provided between the organic compound layer 1226 and theanode 1228. As materials for forming a barrier layer, material shown inEmbodiment 1 is used.

[0274] According to above-mentioned, a light emitting device havingreverse stagger TFT can be formed. The light emitting device formed bythis embodiment can emit light at the direction indicated by the arrow(upward) shown in FIG. 12B.

[0275] A manufacturing steps of the reverse stagger TFT is easier toreduce than that of the top gate TFT. It has an advantages in reductionof manufacturing cost.

[0276] In this embodiment, upward emission light emitting device havingreverse stagger TFT that emit light from an anode side of the lightemitting element. The present invention can be implemented by combiningthe reverse stagger TFT with downward emission type that emit light froman anode side of the light emitting element and upward emission typethat emit light from a cathode side of the light emitting element.

[0277] [Embodiment 6]

[0278] Being self-luminous, a light emitting device using a lightemitting element has better visibility in bright places and widerviewing angle than liquid crystal display devices. Therefore, displaydevices of various electric appliances can be completed by using thelight emitting device of the present invention.

[0279] Given as embodiments of an electric appliance that employs alight emitting device manufactured in accordance with the presentinvention are video cameras, digital cameras, goggle type displays (headmounted displays), navigation systems, audio reproducing devices (suchas car audio and audio components), notebook computers, game machines,portable information terminals (such as mobile computers, cellularphones, portable game machines, and electronic books), and imagereproducing devices equipped with recording media (specifically, deviceswith a display device that can reproduce data in a recording medium suchas a digital video disk (DVD) to display an image of the data). Wideviewing angle is important particularly for portable informationterminals because their screens are often slanted when they are lookedat. Therefore it is preferable for portable information terminals toemploy the light emitting device using the light emitting element.Specific embodiments of these electric appliance are shown in FIGS. 14Ato 14H.

[0280]FIG. 14A shows a display device, which is composed of a case 2001,a support base 2002, a display unit 2003, speaker units 2004, a videoinput terminal 2005, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2003. Since the light emitting device having the light emitting elementis self-luminous, the device does not need back light and can make athinner display unit than liquid crystal display devices. The displaydevice refers to all display devices for displaying information,including ones for personal computers, for TV broadcasting reception,and for advertisement.

[0281]FIG. 14B shows a digital still camera, which is composed of a mainbody 2101, a display unit 2102, an image receiving unit 2103, operationkeys 2104, an external connection port 2105, a shutter 2106, etc. Thelight emitting device manufactured in accordance with the presentinvention can be applied to the display unit 2102.

[0282]FIG. 14C shows a notebook personal computer, which is composed ofa main body 2201, a case 2202, a display unit 2203, a keyboard 2204, anexternal connection port 2205, a pointing mouse 2206, etc. The lightemitting device manufactured in accordance with the present inventioncan be applied to the display unit 2203.

[0283]FIG. 14D shows a mobile computer, which is composed of a main body2301, a display unit 2302, a switch 2303, operation keys 2304, aninfrared port 2305, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2302.

[0284]FIG. 14E shows a portable image reproducing device equipped with arecording medium (a DVD player, to be specific). The device is composedof a main body 2401, a case 2402, a display unit A 2403, a display unitB 2404, a recording medium (DVD or the like) reading unit 2405,operation keys 2406, speaker units 2407, etc. The display unit A 2403mainly displays image information whereas the display unit B 2404 mainlydisplays text information. The light emitting device manufactured inaccordance with the present invention can be applied to the displayunits A 2403 and B 2404. The image reproducing device equipped with arecording medium also includes home-video game machines.

[0285]FIG. 14F shows a goggle type display (head mounted display), whichis composed of a main body 2501, display units 2502, and arm units 2503.The light emitting device manufactured in accordance with the presentinvention can be applied to the display units 2502.

[0286]FIG. 14G shows a video camera, which is composed of a main body2601, a display unit 2602, a case 2603, an external connection port2604, a remote control receiving unit 2605, an image receiving unit2606, a battery 2607, an audio input unit 2608, operation keys 2609, eyepiece portion 2610 etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2602.

[0287]FIG. 14H shows a cellular phone, which is composed of a main body2701, a case 2702, a display unit 2703, an audio input unit 2704, anaudio output unit 2705, operation keys 2706, an external connection port2707, an antenna 2708, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2703. If the display unit 2703 displays white letters on blackbackground, the cellular phone consumes less power.

[0288] If the luminance of light emitted from organic materials israised in future, the light emitting device can be used in front or rearprojectors by enlarging outputted light that contains image informationthrough a lens or the like and projecting the light.

[0289] These electric appliances now display with increasing frequencyinformation sent through electronic communication lines such as theInternet and CATV (cable television), especially, animation information.Since organic materials have very fast response speed, the lightemitting device is suitable for animation display.

[0290] In the light emitting device, light emitting portions consumepower and therefore it is preferable to display information in a mannerthat requires less light emitting portions. When using the lightemitting device in display units of portable information terminals,particularly cellular phones and audio reproducing devices that mainlydisplay text information, it is preferable to drive the device such thatnon-light emitting portions form a background and light emittingportions form text information.

[0291] As described above, the application range of the light emittingdevice manufactured by using the deposition device of the presentinvention is so wide that it is applicable to electric appliances of anyfield. The electric appliances of this embodiment can employ as theirdisplay units any light emitting device which is formed by implementingEmbodiments 1 to 5.

[0292] The edge portions of a first electrode of a light emittingelement can be covered by an insulating layer in accordance withimplementing the present invention, and therefore electric fieldconcentrations from the edge portions of the first electrode to anorganic compound layer can be prevented from occurring when applying avoltage to the light emitting element, and deterioration of the organiccompound layer which develops following the electric field concentrationcan be prevented. Further, the insulating layer formed in the presentinvention is formed such that steps with the first electrode do notdevelop, and therefore film formation irregularities of the organiccompound layer formed on the first electrode can be prevented.

What is claimed is:
 1. A method of manufacturing a light emittingdevice, comprising: forming a thin film transistor over a substrate;forming an insulating layer over the thin film transistor; forming awiring over the insulating layer; forming a conductor, which iselectrically connected to the thin film transistor by the wiring, overthe insulating layer; forming an insulating film over the conductor;polishing the conductor and the insulating film by a chemical mechanicalpolishing method, thus forming a first electrode and a leveledinsulating layer; forming an organic compound layer contacting the firstelectrode; and forming a second electrode contacting the organiccompound layer; wherein the first electrode and the leveled insulatingfilm formed by the chemical mechanical polishing method form the sameplane.
 2. A method according to claim 1, wherein the first electrode andthe leveled insulating film formed by polishing by a chemical mechanicalpolishing method have a film thickness of from 50 to 500 nm.
 3. A methodof manufacturing a light emitting device, comprising: forming a thinfilm transistor on a substrate; forming an insulating layer covering thethin film transistor; forming a wiring through the insulating layer;forming a conductor, which is electrically connected to the thin filmtransistor by the wiring, on the insulating layer; forming an insulatingfilm covering the conductor; polishing the conductor and the insulatingfilm by a chemical mechanic polishing method, thus forming a firstelectrode and a leveled insulating layer; forming an organic compoundlayer contacting the first electrode; and forming a second electrodecontacting the organic compound layer; wherein the organic compoundlayer is formed so as to completely cover the first electrode.
 4. Amethod according to claim 3, wherein the first electrode and the leveledinsulating film formed by polishing by a chemical mechanical polishingmethod have a film thickness of from 50 to 500 nm.
 5. A method ofmanufacturing a light emitting device, comprising: forming a thin filmtransistor on a substrate; forming an insulating layer covering the thinfilm transistor; forming a wiring through the insulating layer; forminga conductor, which is electrically connected to the thin film transistorby the wiring, on the insulating layer; forming an insulating filmcovering the conductor; polishing the conductor and the insulating filmby a chemical mechanical polishing method, thus forming a firstelectrode and a leveled insulating layer; forming an organic compoundlayer contacting the first electrode; and forming a second electrodecontacting the organic compound layer; wherein the organic compoundlayer is formed contacting the first electrode and the leveledinsulating layer.
 6. A method according to claim 5, wherein the firstelectrode and the leveled insulating film formed by polishing by achemical mechanical polishing method have a film thickness of from 50 to500 nm.
 7. A light emitting device comprising: a first electrode havingan edge portion; a leveled insulating film formed contacting the edgeportion of the first electrode; an organic compound layer adjacent tothe first electrode; and a second electrode adjacent to the leveledinsulating layer and the organic compound layer; wherein surfaces of thefirst electrode and the leveled insulating layer are coplanar.
 8. Adevice according to claim 7, wherein the first electrode comprises amaterial having light transmittance and functions as an anode.
 9. Adevice according to claim 7, wherein the second electrode comprises amaterial having light transmittance and functions as an anode.
 10. Adevice according to claim 9, further comprising a barrier layer betweenthe organic compound layer and the second electrode.
 11. A deviceaccording to claim 7, wherein the second electrode comprises a materialhaving light transmittance and functions as a cathode.
 12. A deviceaccording to claim 11, wherein: the second electrode is formed bylaminating a material belonging to one of Group 1 and Group 2 of theperiodic table and a material having conductivity.
 13. A deviceaccording claim 7, wherein the light emitting device is one typeselected from the group consisting of: display devices; digital stillcameras; notebook personal computers; mobile computers; portable imageplayback devices prepared with a recording medium; goggle type displays;video cameras; and mobile phones.
 14. A light emitting devicecomprising: a thin film transistor formed over a substrate; a wiring; afirst electrode having an edge portion, the first electrode electricallyconnected to the thin film transistor through the wiring; a leveledinsulating layer formed contacting the edge portion of the firstelectrode; an organic compound layer formed contacting the firstelectrode; and a second electrode formed adjacent to the leveledinsulating layer and the organic compound layer; wherein surfaces of thefirst electrode and the leveled insulating layer are coplanar.
 15. Adevice according to claim 14, wherein the first electrode comprises amaterial having light transmittance and functions as an anode.
 16. Adevice according to claim 14, wherein the second electrode comprises amaterial having light transmittance and functions as an anode.
 17. Adevice according to claim 16, further comprising a barrier layer betweenthe organic compound layer and the second electrode.
 18. A deviceaccording to claim 14, wherein the second electrode comprises a materialhaving light transmittance and functions as a cathode.
 19. A deviceaccording to claim 18, wherein: the second electrode is formed bylaminating a material belonging to one of Group 1 and Group 2 of theperiodic table and a material having conductivity.
 20. A deviceaccording claim 14, wherein the light emitting device is one typeselected from the group consisting of: display devices; digital stillcameras; notebook personal computers; mobile computers; portable imageplayback devices prepared with a recording medium; goggle type displays;video cameras; and mobile phones.